Electrical apparatus for gas and vapor testing



July 3, 1956 E. c. GREANIAS ET AL 2,753,247

ELECTRICAL APPARATUS FOR GAS AND VAPOR TESTING Filed 001*. 27, 1950 FLASH POINTIOF SAMPLE (F) g 0.4 0.G 0.8 L0 L2 L4 1.6

Samgle RATIO OF READINGS Clo H22 5 9 ZIZL 1 514 42 INVENTORS: Evan C. Grean/as F j Roberfidacobs "/119 BY United States Patent IiLECTRICAL APPARATUS FOR GAS AND VAPOR TESTING E'von C. Greanias, Chicago, and Robert B. Jacobs, Homewood, 11]., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana Application October 27, 1950, Serial No. 192,515

3 Claims. 01. 23 zs This invention relates to improvements in apparatus of the type wherein the temperature and resistance of a heated filament in an electrical circuit are varied by the character of a fluid surrounding the filament and relates to a portable filament apparatus wherein changes in the resistance of the filament are measured by means of an electrical system. More specifically the invention pertains to a portable arm of a Wheatstone bridge useful in the determination of the flash point of hydrocarbon liquids.

We have devised a system for automatically obtaining an indication of the flash point of liquids by means of an apparatus comprising a Wheatstone bridge in adjacent arms of which are placed identical filaments of a material'which is a catalyst for oxidation of vapors. One is the test filament exposed to oil vapors and the other is a reference filament which is not. Catalytic oxidation of the oil vapors raises the temperature of the exposed test filament. This results in a change in the ratio of the filament resistances producing an unbalance of the bridge which is correlated with flash points as described in our copending application Serial No. 192,516, filed October 27, 1950, entitled Flash Point Determination and Recording.

By our system, a large number of samples are tested in series atthe same constant temperature, each sample being placed in a partially filled container or flask which is closed and immersed in a constant temperature bath. When the sample vapor has come to equilibrium at the bath temperature, the heated test filament is inserted into the vapor space of the sample container and combustion occurs at the test filament causing its temperature to rise above that of the reference filament similarly heated by the electric current but not exposed to combustible vapors.

The rise in the test filament temperature depends upon f the rate of combustion and the resulting unbalance of the Wheatstone bridge circuit is correlated with the flash point of the sample. This can be done by comparing the extent of observed unbalance of the bridge with that which occurs when decane or another standard hydrocarbon of known flash point is tested under identical conditions. -Thecuccessful determination of flash points by this type of system depends essentially upon the physical uniformity and stability of the comparative filaments. When the temperature of the test filament increases during the catalytic oxidation thereon, it increases in length and when subjected to mechanical shock may change its shape. Either or both of these effects will result in a change in the electrical characteristics of the filament.

Heretofore it has been proposed to stretch the filaments between fixed points in the test chamber or to use helical filaments. However, these have not produced a satisfactorily stable filament for portable use. It is therefore a primary object of this invention to provide a portable filament mounting which provides uniform shape at varying temperatures and under mechanical shock. Another ob ject is to provide a filament assembly which can be manipulated so as to enter the narrow mouth of a container or flask containing a sample to be tested for flash point. A more specific object of the invention is to provide a rugged filament mounting or probe adapted to be inserted within a test flask. These and other objects of the invention will become apparent as the description thereof proceeds.

Briefly, according to the invention, we provide a springloaded straight platinum filament. The filament is supported by a pair of mounting springs in tension. The mounting springs are in turn fixed to conductor posts in a generally cylindrical insulating body encased within a brass sleeve and electrical conductor elements are connected to the posts. The sleeve is adapted to be inserted within a test flask, thereby placing the filament within the flask in a zone which is at equilibrium with regard to temperature and vapor concentration.

It is essential to have the filament in a horizontal or transverse position with respect to the longitudinal axis of the probe. This places the entire filament near and at a uniform height above the surface of the liquid sample in the flask and avoids vapor pressure and temperature gradients which might occur. The brass sleeve is so arranged to insure that the transverse filament assumes a uniform height when inserted into the test chambers.

Further details of the invention are illustrated by the accompanying drawings wherein:

Figure 1 is a longitudinal sectional view of our novel filament holder or probe;

Figure 2 is a schematic showing of one apparatus employing our test method or probe; and

Figure 3 illustrates a chart correlating flash points to the bridge unbalance.

Referring to Figure 1, the details of our probe are illustrated. The catalytic filament 10 may for example be a platinum filament of about 0.003 inch diameter and about 0.266 inch in length and mounted between mounting springs 11 under a tension of about 3.5 grams. The leaf springs 11 maybe of stainless steel of about 0.375 inch in length and 0.04 x 0.031 inch in cross section and supported at their ends by posts 12 made of conducting metal, such as copper, clad with chemically inert material as the application requires and embedded in a generally cylindrical and elongated body portion 13 made of insulating material such as Lucite. A brass sleeve 14 surrounds the lower portion of the body 13 and this sleeve is adapted to enter the throat 15 of the flask or sample container 16. A shielded cable 17 having conductors 18 and 19 passes through cable spring 20 anchored in nut 21 which is threaded about the cylindrical cable connector shield 22 encircling a substantial proportion of the body 13 and separated from sleeve 14 by annular shoulder 23 on body 13. The conductors 18 and 19 are electrically connected to the copper posts 12. A protective cage having bars 24 extending longitudinally from the sleeve 14 to a ring 25 is provided to prevent damage to the mounting springs 11 and the filament 10.

A pair of probes 30 and 31 of the type illustrated in Figure 1 are connected in the electrical circuit illustrated in Figure 2. A direct current power source to furnish the necessary heating current of about 0.75 amps may comprise transformer 32 and rectifier 33, the output of which is applied to the circuit including ammeter 34, variable resistances 35 and 36, fixed resistance 37, filaments 10 and 10a and the associated conductors. The output of the bridge circuit is transmitted by leads 38 and 39 to an indicator or recorder means (not shown).

A shallow and wide constant temperature bath 45 holds a number of containers 16, 46 and 47 mounted on rack 48 within the bath as shown in Figure 2. The bath temperature determines the useful flash point range of the instrument and, in general, this range is limited to about 75 F. Above the bath temperature since beyond such upper limit, sensitivity diminishes rapidly. The maximum temperature variation between any two points in the bath at any time is kept less than about 0.4 F. by circulation of the bath liquid and a stirrer (not shown) may be used for that purpose.

Preliminary to making a flash point determination employing our apparatus, the oil is placed in the bath 45 to the indicated level below the mouth of the flask or container 16 and the temperature of the oil is brought to about 100 F. The container rack 48 is fitted with sample reference, and check containers 16, 46 and 47. The check container 47 contains 20 cc. of pure decane and is used to determine the sensitivity of the test probe 31. Reference container 46 is an empty clean container in which the reference probe is ordinarily kept permanently.

To test a group of samples, a number of sample containers are carefully cleaned so that no trace of previous samples or solvent remains. Satisfactory results have been obtained by thoroughly rinsing the containers with carbon tetrachloride and drying with an air stream before filling. Exactly 20 cc. of the sample is placed in each sample container such as 16 and immediately corked. These sample containers are then placed in the bath 45.

The reference probe 30 is kept in an empty container 46 in the bath to maintain it at the ambient filament temperature. The output of the Wheatstone bridge is applied to a high precision indicator which may be a voltmeter, an alarm system, or a recorder.

A large number of tests were made with the catalytic filament on samples of known flash points and the ratios of the recorder readings of the sample and of the standard were plotted to provide the curve of Figure 3. The flash points of other blended samples were determined by precision tag closed cups and these check points fell well within the points obtained earlier. Thus when the ratio of the sample reading to the check reading obtained with pure decane is applied to the curve, the flash point can be read ofi directly. Alternatively, calibration charts have been prepared wherein the deflections of the recorder for given probe sensitivity, as determined with decane, are plotted against flash point. Thus, the observed deflection reading with an unknown can be applied to the calibration curve and the flash point read from the chart.

In general, a platinum filament is satisfactory but in some instances the inherent strength of a catalytic filament which consists of an alloy containing at least one of the elements of the platinum group including rhodium, palladium, ruthenium, and iridium may be preferred. For example a 10 percent rhodium alloy of platinum has been used satisfactorily with a 0.003 inch filament.

Although our invention has been described in terms of specific apparatus which is described in considerable detail, it should be understood that this is by way of iilustration only and that the invention is not necessarily limited thereto, since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of the disclosure. Accordingly, modifications in the invention are contemplated without departing from the spirit of the described invention or the scope of the appended claims.

We claim:

1. In a test apparatus adapted to have one end thereof inserted into a test chamber and forming one arm of a Wheatstone bridge circuit, the improved probe which comprises an electrically non-conducting core of generally cylindrical configuration, an annular shoulder on said core intermediate the ends thereof, a sleeve encircling a first portion of said core and terminating adjacent an end thereof, a shoulder on said sleeve abutting said shoulder on said core, a pair of electrically conducting posts spaced from each other and extending longitudinally through said core, extensions of said posts projecting beyond the end of said first portion of said core encircled by said sleeve, a pair of electrically conductive resilient supports carried by the projecting extensions of said posts, a catalytic filament supported in tension between free ends of said resilient supports transverse to the longitudinal axis of said core, electrical leads connected to said posts, a connector shield encircling a second portion of said core and projeting beyond the end thereof, a connector shield nut threaded to said connector shield and having an aperture therein through which said electrical leads pass, and a protective cage carried by said sleeve and projecting longitudinally beyond the ends of said resilient supports so as to protect said supports and said filament.

2. An improved probe for use in a testing apparatus which comprises an electrically non-conducting core of generally elongated configuration, a shoulder about the girth of said core, a casing about a first portion of said core and terminating adjacent an end thereof, a shoulder on said casing abutting said shoulder on said core, a pair of electrically conducting posts spaced from each other and extending longitudinally through said core, extensions of said posts projecting beyond the end of said first portion of said core enclosed by said casing, a pair of electrically conductive resilient supports carried axially by the projecting extensions of said posts, a catalytic filament supported in tension between the other ends of said resilient supports and extending transversely to the longitudinal axis of said core, electric leads connected to said posts remote from said projecting extensions, a connector shield enclosing a second portion of said core and projecting beyond the end thereof, and a protective cage carried by said casing and projecting longitudinally beyond the ends of said resilient supports so as to project said supports and said filament.

3. The apparatus of claim 2 wherein the protective cage comprises a plurality of peripheral wire elements terminating beyond said filament in a ring having an outside diameter which is smaller than the outside diameter of said casing.

References Cited in the file of this patent UNITED STATES PATENTS 1,231,045 Means June 26, 1917 1,756,793 Mabbs et al. Apr. 29, 1930 2,013,998 Goldsborough Sept. 10, 1935 2,393,220 Jacobson et al. Jan. 15, 1946 FOREIGN PATENTS 697,662 France Nov. 4, 1930 

2. AN IMPROVED PROBE FOR USE IN A TESTING APPARATUS WHICH COMPRISES AN ELECTRICALLY NON-CONDUCTING CORE OF GENERALLY ELONGATED CONFIGURAION, A SHOULDER ABOUT THE GIRTH OF SAID CORE, A CASING ABOUT A FIRST PORTION OF SAID CORE AND TERMINATING ADJACENT AN END THEREOF, A SHOULDER ON SAID CASING ABUTTING SAID SHOULDER ON SAID CORE, A PAIR OF ELECTRICALLY CONDUCTING POSTS SPACED FROM EACH OTHER AND EXTENDING LONGITUDINALLY THROUGH SAID CORE, EXTENSIONS OF SAID POSTS PROJECTING BEYOND THE END OF SAID FIRST PORTION OF SAID CORE ENCLOSED BY SAID CASING, A PAIR OF ELECTRICALLY CONDUCTIVE RESILIENT SUPPORTS CARRIED AXIALLY BY THE PROJECTING EXTENSIONS OF SAID POSTS, A CATALYTIC FILAMENT SUPPORTED IN TENSION BETWEEN THE OTHER ENDS OF SAID RESILIENT SUPPORTS AND EXTENDING TRANSVERSELY TO THE LONGITUDINAL AXIS OF SAID CORE, ELECTRIC LEADS CONNECTED TO SAID POSTS REMOTE FROM SAID PROJECTING EXTENSIONS, A CONNECTOR SHIELD ENCLOSING A SECOND PORTION OF SAID CORE AND PROJECTING BEYOND THE END THEREOF, AND A PROTECTIVE CAGE CARRIED BY SAID CASING AND PROJECTING LONGITUDINALLY BEYOND THE ENDS OF SAID RESILIENT SUPPORTS SO AS TO PROJECT SAID SUPPORTS AND SAID FILAMENT. 